Demister Apparatus and Method

ABSTRACT

A demister apparatus for machine tools having an enclosure booth for confining mist in which a varying outflow of air is drawn from the booth and directed to a remote demister apparatus from a minimum when the access doors to the enclosure are closed to a maximum when one or more of the doors are opened. The air flow may also be varied with the number of machine tools in operation as well with the state of filters in the remote demister apparatus. A cyclonic separator is also provided adjacent to the booth which functions well in a vertical up flow mode over a range of air outflow rates of flow.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Ser. No. 61/913,553 filed on Dec. 9, 2013.

BACKGROUND OF THE INVENTION

In automated machining of parts such as engine components, the machining takes place at machine stations, each station enclosed to form a booth. A coolant/lubricant liquid is sprayed onto the part during the machining operations in order to reduce friction and cool the part.

This spraying creates a fine mist which is intended to be confined within the booth in order to prevent the mist from being dispersed into the air within the plant, where it could be inhaled by plant personnel and present a health hazard. Also, the mist can condense onto adjacent surfaces, creating a maintenance burden.

Oil in the coolant/lubricant can also evaporate from the mist into the air and create an air pollution problem.

In order to minimize this effect, the conventional practice has been to constantly draw a large volume of air out of the booths and into ducting with a fan driven by a powerful electric motor drawing considerable power. This is intended to prevent the mist from dispersing into the air in the plant. The ducting leads to a central filter/demister where the mist is completely removed from the air before being discharged back into the atmosphere.

The coolant/lubricant condensed from the mist is collected and directed back to the machine station for reuse.

It has heretofor been recognized that it is advantageous to remove as much mist as possible at a location close to the machine tool station rather than transporting all of it to a central demisting location in order to reduce the quantity of mist transported through the ducting to the central unit. This is because leaking of condensed mist from the ducting, and evaporation of the oil in the mist into the air can both occur in the ducts, which effects will contribute to the air pollution problem mentioned above. In addition, condensed water can aid the growth of mold and creation of a fire hazard. Also, less mist flowing in the ducts reduces the maintenance efforts required in cleaning the ducting through which the mist flows.

Furthermore, high efficiency air filters (HEPA) are used to completely remove the residual mist, and these filters would rapidly become blocked if all of the mist were to reach those filters, greatly increasing maintenance costs since HEPA filters are very expensive.

A decentralized demister arrangement is described in U.S. Pat. Nos. 8,266,945 and 7,727,295, incorporated herein by reference, as well as in a TMI brochure published in 2002, referenced in those patents.

The volume of air flow drawn out of a CNC machine booth is conventionally set at a high flow rate which is thought necessary to prevent escape of oily mist from the machining booth at any time during the machine cycle, and also to insure proper operation of the cyclonic separator.

That is, the cyclonic separators typically used have usually required high air flow rates through them in order to be effective.

It is an object of the present invention to provide a demister arrangement for machine tool installations which greatly reduces the power consumption required while insuring that no mist escapes from the machining booth at any time.

SUMMARY OF THE INVENTION

The above recited object as well as other objects which will be understood by those skilled in the art upon a reading of the following specification and claims is achieved by reducing the rate of air flow drawn from the machining booth to that minimally necessary to insure that no mist escapes the machine tool booth. This is achieved by varying the volume of air flow drawn out from the booth to a low level which is all that will be needed during those periods when the access doors to the machining center booth enclosure are closed, to a maximum air flow drawn from the booth when the doors are opened, as when loading and removing parts being machined in the station.

The differing out flow rates are preferably achieved by using a variable frequency drive (VFD) control on a fan motor used to draw air from the booth, to significantly reduce the total power consumption of the fan motor by reducing the power to the fan motor from a level when full output is required to a reduced level of air flow out adequate to maintain a vacuum level in the booth. This will insure that no mist containing air escapes from the enclosure booth at any time during the machining operation.

It has been determined that a particular cyclonic separator of a type described in U.S. Pat. No. 7,311,744, incorporated herein by reference when operated in a “vertical up” mode has the capability of operating successfully to remove mist over the range of air outflow rates through the separator which is necessary to substantially minimize power consumption of the fan motor over the machine cycle.

A similar situation is presented in a multi-station installation, when the fan motor conventionally is set to always run to produce the air outflow rate necessary to prevent out flow of booth air, when all stations are operating. In the present invention, an automatic step down of the fan motor operation is carried out if fewer machining stations are on line, so that a significantly lower air out flow rate will suffice, to also conserve power.

Additionally, the fan motor may be controlled to vary in correspondence to the flow resistance encountered in the demister filters, i.e., the fan motor power can set at a minimal level when the filters are clean and increased as the HEPA and/or other filters at the central demister become more clogged.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a machining booth with a connected demister/filter apparatus and a block diagram representation of associated controls therefore according to the present invention.

FIG. 1A is an enlarged sectional view of a typical duct joint showing a sealed connection.

FIG. 2 is a diagram of a second stage demister/filter with block diagram depiction of control sensor components.

FIGS. 3A, 3B and 3C are diagrams of alternative control schemes which could be utilized to vary the fan motor power.

FIG. 4 is a plot of efficiency versus air flow rate of the cyclonic separator used in the apparatus and method of the present invention.

FIG. 5 is a side view of the cyclonic separator as used in the invention.

FIG. 5A is a longitudinal cross section of the cyclonic separator shown in FIG. 5.

FIGS. 6 and 7 are downstream and upstream end views, respectively, taken along the lines 6-6 and 7-7 in FIG. 5.

FIG. 8 is a perspective view of the cyclonic mist separator shown in FIGS. 5-7, with portions of the cyclonic mist separator housing being cut-away for clarity to showing certain internal components.

DETAILED DESCRIPTION

In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims.

Referring to FIG. 1, a machining center booth 10 is shown which encloses a conventional automated CNC machining station (not shown) in which parts are machined with the use of metal cutting tools in the well known manner.

The parts are typically unloaded after one or more access door panels 12 are opened, as indicated in FIG. 1 by load/unload robots or other part handling devices (not shown), which then load parts to be machined into the machines, with the access door panels then closed.

As noted, such machining operations use metal cutting tools which involve the use of cutting fluids sprayed on the part and tools in the well known manner. This generates mist such as from oil, water vapor, synthetic coolant, etc. which is designed to be confined within the booth 10 in order to prevent the mist from escaping into the surrounding air where it would present the various problems referred to above.

This is done conventionally by continuously drawing the air into which the mist has dispersed out from booth 10 and into ducting 14 by operation of a blower 16 which is driven by a powerful electric motor 18 (FIG. 2). The blower 16 may be contained within a central separator/filter apparatus 20.

This is air flow drawn out of the machining center booth is continuously maintained so as to make certain that none of the mist containing air escapes the confines of the machining center booth 10 except dispersed in this flow of air drawn out by the blower 16.

As described above, it is now known that it is desirable to remove as large proportion of the mist at points close to each booth 10, rather than directing the mist laden air to a central filter/demister before removing any of the mist, as was the former practice.

Again, this is because movement of the air containing the mist through long ducts increases the evaporation of oils into the atmosphere to create air pollution, and finally, partially condenses the mist therein, to create a fire hazard, and mold growth, creates a maintenance burden due to the necessity for regular cleaning of the ducts. This also necessitates pumping of condensed coolant back to the machining stations for reuse.

Thus, it is now common practice to install a first stage separator 22 immediately above the enclosure 10, which collects condensed mist liquid that is drained back into the reservoir of cutting fluids in the machine tool in the booth 10, as by gravity via a drain line 24.

Referring to FIG. 2, the details of a central demister/filter apparatus 20 are shown with the fan motor 18 and fan 16 mounted within a housing 56 located above aluminum mesh washable prefilter 58; and 95% DOP HEPA filter 64. The top insures substantially all of the mist is removed from the air flow prior to its discharge into the outlet 66 and thence into the atmosphere.

The air inlet 53 (connected to ducting 14), receives air flow at a point below the prefilter 58 and is drawn up by operation of the blower 16.

Condensed mist drawn from the prefilter 58 and final filter 64 is collected at the bottom of the housing 55 and drains back by gravity or is pumped back to the station via pipe 65 (FIG. 1).

The machine control 70 receives a signal from a sensor (not shown) detecting when the panels 12 are open or closed such that a variable frequency (VFD) 72 drive control is operated to normally run the fan motor 18 at a substantially reduced power setting which is still adequate to maintain vacuum levels exist within the booth 10 to present the escape of air, i.e., when the panels 12 are closed, and at a stepped up power level only when the access door panels 12 are opened.

There are several ways contemplated by the present invention to determine when and to what extent the air flow drawn out of the booth 10 must be varied over the course of operation of the machining station to achieve the benefits of the present invention.

Firstly and preferably, the machine controls 70 transmits a signal to the VFD drive control 72 when the door panels 12 are about to be opened by the machine controls 70 for the unloading and loading of parts, such that the blower motor 18 power can be stepped up to a much higher level, predetermined to be adequate to reliably insure mist containing air will not escape from the booth 10.

This approach allows anticipation of the need for increased air flow so that the shift to a higher flow rate can be initiated before the access door panels open and thus actually be developed by the time the door panels 12 are opened.

This requires integration with the machine controls 70 which may require the cooperation of those responsible for the machine tool operation.

An alternative approach is depicted in the arrangement of FIG. 3A, in which changes in air flow are sensed such as by measuring the pressure drop across the first stage separator 22 with a differential pressure sensor 74 connected to pressure taps 76 on either end of the separator 22.

As the door panels 12 begin to open, the air flow and pressure drop will begin to increase due to the reduced restriction of the air flow entering the booth 10. In response, the power level of the fan motor 18 is correspondingly ramped up, set by a control 78 acting on the VFD 72.

Such sensor differential pressure can be measured anywhere in the system to detect increases in the air flow drawn out of the machining center booth 10.

Another alternative approach is depicted in FIG. 3B, where one or more vacuum sensors 80, 82 are provided within the machining center booth 10 at one or more locations therein in order to sense vacuum level changes anywhere within the machining center booth 10.

As the access door panels 12 begin to open, the vacuum level within the enclosure booth 10 will begin to lessen, i.e., the pressure in the booth 10 will begin to increase, so that the vacuum level will begin to decline.

This reading will be sent to control 78 which acts on the VFD to cause a corresponding increase in power of the blower motor 18 as in FIG. 3A as necessary to maintain the vacuum level.

As the vacuum level start to move higher as the door panels 12 begin to close, this is sensed by the sensors 80, 82 and the air flow rate reduced accordingly.

FIG. 3C shows yet another alternative approach in which a switch 84 is associated with one or more of the access door panels 12 which generate when the associated access door panel 12 begins to open. Again, this causes the control 78 to generate a signal transmitted to the VFD 72 increasing the power to the blower 18 to increase the outflow of air from the enclosure booth 10.

Other arrangements may be used that will achieve this same result.

The mist separator 22 is advantageously of a particular cyclonic design generally described in U.S. Pat. No. 7,311,744, although in a modified form.

It has been discovered that such a separator particularly as modified can function successfully to remove a high proportion of mist from the air flow directed therethrough over a substantial range of air flow rates through the separator 30 such that considerable variations in the rate of flow of the air being drawn through the separator 30 is possible while maintaining a high degree of demisting at the enclosure booths 10.

Referring to FIGS. 5-10, the separator 30 includes a cylindrical, tubular housing 32 that defines a cylindrical inside wall 34 (see FIGS. 5-7), and that is connected between aligned inlet and exit end couplings 36 b and 36 a provided with associated inlet 96 and exit 97 openings and adapted for connection to the ducting 14 such that mist contaminated air enters as indicated at 40 g and pre-cleaned air exits as indicated at 40 a.

Internal stationary vanes 38 are connected in the upstream and downstream end portions of the housing 32. The vanes 38 are sized and positioned to establish and maintain a cyclonic air flow pattern such as indicated at 40 b downstream thereof. The cyclonic flow causes the moisture to migrate outwardly as indicated at 40 c to the inside wall 34, and to flow downwardly along the surface of the inside wall 34 as indicated at 40 d. To this end, a separation chamber 56 is defined between the vanes, generally in the center portion of the housing, and is characterized as being of generally open, unobstructed construction as shown for maximum separation of moisture from the swirling air flowing therethrough.

In preferred embodiments, the vanes 38 are used at both the upstream and downstream ends. Between the inside wall 34, longitudinally spaced center supports 52 a, 52 b provide for relatively stiff cyclonic-flow vane structure.

A liquid collection chamber 42 is located at the bottom portion of the separator 30 to collect the liquid flowing along the inside wall 34, and to direct the liquid to a drain 44. The liquid collection chamber also establishes a barrier to prevent the liquid from being sucked back into the air as it exits the separator such that, once the liquid enters the chamber, it is generally trapped therein. The collection chamber is an annular, dead-ended space provided with an annular entrance opening that is coincident with the inside wall 34 of the housing such that liquid flowing in the upstream direction along the inside wall of the separation chamber flows directly into the collection chamber as indicated at 40 e.

The collection chamber may be defined between the outside diameter (OD) of an inlet tube 48 that extends in the downstream direction from the inlet coupling 96, the inside diameter (ID) of the housing wall 34, a downstream end wall 54 b of the housing. For separators as here intended to be used in a generally vertical orientation, the drain hole 44 is preferably positioned with its downstream open edge coincident with or slightly downstream of the radially outer edge of the end wall 54 b (to the left as shown in FIG. 5) to preclude a dead-space behind the drain hole in which liquid cold accumulate.

In the collection chamber 42, the liquid continues to flow in a generally circular pattern such as indicated at 40 f in FIG. 6. Upon reaching the downstream end and bottom of the collection chamber, circulation of the liquid is interrupted by a flow-interrupter 50 that projects into the collection chamber in the downstream end portion proximate the downstream wall 54 b. The flow interrupter is shaped to direct the liquid flowing around the collection chamber to the drain 44. The flow interrupter is preferably provided in the form of a generally radially inwardly extending wall portion that breaks the swirling flow at the drain.

To this end, the flow interrupter is connected or located just downstream of the drain with respect to the swirling flow of liquid therein, and is provided in a form that includes at least a first portion that projects generally longitudinally along the wall 34. In preferred embodiments, the flow interrupter is further provided with a second portion that extends generally substantially circumferentially from the first portion such as the L-shaped hood shown that extends over and above the drain hole, or in the form of a curved-hood that curves over and above the drain hole. It has been found that, in most instances encountered, the hood extending to a position over the drain hole is preferred as providing better direction of the liquid into the drain as compared with, for example, a straight interrupter consisting of only the first generally radially projecting portion.

For use in existing mist collection systems, the separator 30 is preferably adapted for relatively low air pressure drop. This allows use of the separator to be used within the air-flow capacity of the fan of the existing system. To this end, the separator may be provided with upstream and downstream annular walls 54 a, 54 b that extend radially outwardly from associated inlet and exit couplings 36 b, 36 a proximate the inlet and exit openings, and the inside wall 34 extends therebetween to define an upstream expansion chamber into which the air flow enters upon flowing through the inlet opening and in which stationary vanes are located, the inside diameter of the wall 34 being preferably approximately one-fourth to one-third larger than the diameter of the hoses and end couplings 36 a, 36 b (i.e., the diameter of the inlet and exit openings) for a relatively low pressure drop embodiment.

By way of dimensional example, one of the common size hoses currently used in mist collectors are six inch hoses. In this instance, it has been found that a cylindrical wall ID of eight inches, with end coupling of six inches diameter, provides relatively low pressure drop; and that for vanes extending longitudinally approximately four and one-hale (4½) inches, with the leading edges set at an angle of approximately 25 degrees with respect to the upstream opening face (as seen in FIG. 5), and extending longitudinally therefrom at an angle of approximately 35 degrees with respect to a longitudinal axis therethrough, provides good cyclonic action in the separator.

It has also been found that a flow restrictor adapted to provide a radial clearance of approximately one-fourth (¼) to one-half (½) inch, and preferably three-eighths (%) inch allows the liquid to enter the collection chamber 42, while providing good restriction to prevent the liquid from leaving the chamber. In this example, as well as other similarly sized units such as for eight inch hoses provided with a ten inch ID wall and a flow restrictor cone radial clearance of approximately three-eighths inch, removal of between 85-95% of the mist from the air has been consistently achieved, with a relatively low pressure drop.

It will also be understood, however, that for new design systems where the pressure drop may be permitted to increase or decrease, because the capacity of the fan has not yet been established (as compared to existing mist collections systems with an already installed fan), the dimensional difference between the end couplings and the inside diameter of the housing may be increased or decreased.

It has also been found that the optimum size and number of vanes to establish the desired cyclonic action will vary depending on the size of the cylindrical wall 34. Continuing with the above dimensional examples, it has been found that three vanes of suitable size provide good cyclonic action in a separator with a six inch ID, and five vanes may be required in the larger ten inch housing.

FIG. 3 shows the performance of the cyclonic mist separator 22 over a range of flow rates, showing that effective demisting is achieved over a substantial range of air flow rates, thus allowing the variation in air outflow rates while still achieving effective demisting at the machine. 

1. A demister apparatus for eliminating mist generated in a machining center having an enclosure booth with one or more access door panels which are opened for loading and unloading parts to be machined therein but closed during a cycle of machining of said parts, comprising: an electric motor driven blower arranged to continuously draw a flow of air out of said booth to maintain a partial vacuum in said booth sufficient to prevent the escape of air containing mist from within said booth; an exhaust duct system connected to said blower so as to receive said air flow drawn out of said booth; a demister apparatus remote from said booth including one or more filters connected to said exhaust duct system and including said blower which when operated drawing an air flow out of said booth, said drawn out air flow passing through said one or more filters in said remote demister apparatus and thereafter exhausted through an outlet; a cyclonic demister installed in said exhaust duct system at a location adjacent said machine tool station booth, said air flow drawn out of said booth passed through said cyclonic demister to remove a substantial portion of mist contained therein prior to reaching said remote demister apparatus; and an arrangement increasing the power to said drive blower motor to thereby increase the air flow drawn out of said booth when an increase in air pressure in said booth occurs or is imminent which increase air pressure would otherwise reduce the vacuum level in said booth, said increased in power counteracting the reduced thereof, said arrangement including a VFD controller associated with said blower drive motor, said VFD controller increasing said blower drive motor power in order to increase the air flow drawn out of said booth when air pressure in said booth occurs or is imminent.
 2. The apparatus according to claim 1 wherein said arrangement includes a machine control generating a corresponding signal or signals when one or more of said access panel doors are about to begin to be opened, said signals transmitted to said VFD controller so as to cause said increase in blower drive motor power to produce said increase in said rate of air flow drawn from said booth.
 3. The apparatus according to claim 1 wherein said machining center includes a plurality of machine tools and wherein said VFD controller reduces the power to said motor driven blower when fewer than all of said machine tools are in operation.
 4. The apparatus according to claim 1 wherein a sensor is included detecting the level of blockage in one or more of said filters and wherein said VFD controller increases power to said blower drive motor in response to signals from said sensor corresponding to a predetermined degree of blockage of said one or more filters.
 5. The apparatus according to claim 1 wherein said cyclonic separator comprises: a vertical cylindrical tube provided with an inlet and an exit opening to allow air to be drawn therethrough in an up direction; a set of stationary vanes connected in each of the upstream and downstream portions of the tube and sized and positioned to direct the air flowing therethrough in a cyclonic path through the tube such that mist in the air therein migrates outwardly to and in the downstream direction along the inside wall of the tube; a drain hole positioned near the upstream end of the collection chamber.
 6. The apparatus according to claim 1 wherein said arrangement includes a sensor detecting an increase in said air flow drawn from said booth and generating a corresponding signal transmitted to said VFD controller which increases said power to said blower drive motor correspond.
 7. The apparatus according to claim 1 further including a vacuum sensor associated with said booth generating a corresponding signal transmitted to said VFD controller to increase or decrease the power to said blower drive motor so as to substantially maintain a predetermined vacuum level therein sufficient to substantially prevent the escape of booth air during a machining cycle.
 8. The apparatus according to claim 1 further including a switch arranged to detect opening movement of an access door panel and generate a corresponding output signal which is transmitted to said VFD controller to cause an increase in said blower drive motor power to increase the rate of air flow drawn from said booth upon opening of an access door panel.
 9. A method for eliminating mist generated in a machine tool installation having a booth with one or more access door panels which are opened for loading and unloading parts therein but closed during a cycle of machining of said parts comprising: a blower connected to said booth and operated with a drive motor so as to continuously draw a flow of air out of said booth to maintain a partial vacuum in said booth sufficient to prevent the egress of air containing mist from said booth other than said air flow drawn out of said booth; connecting an exhaust duct system to receive said air flow drawn out of said booth; providing a remote demister apparatus including one or more filters connected to said exhaust duct system receiving said air flow out of said booth and passing said air flow through said one or more filters in said remote demister apparatus and thereafter exhausting said air flow through an outlet; installing a cyclonic demister in said exhaust duct system at a point adjacent said machine tool station booth, said air flow drawn out of said booth passed through said cyclonic demister to remove a substantial portion of mist contained therein prior to entering said remote demister apparatus; and increasing the power to said blower drive motor when an increase in air pressure in said booth occurs or is imminent which would otherwise reduce the vacuum level therein to counteract the effects thereof.
 10. The method according to claim 9 including generating a corresponding signal when one or more of said access panel doors are about to begin to be opened, and transmitting signals to a VFD controller associated with said blower drive motor to cause a corresponding increase in blower drive motor power to in turn increase the rate of air flow drawn from said booth.
 11. The method according to claim 9 wherein said machine tool installation includes a plurality of machine tools and wherein said VFD controller is operated to reduce the power to said blower drive motor whenever fewer than all of said machine tools are in operation.
 12. The method according to claim 9 wherein a sensor is included detecting the level of blockage in one or more of said filters and increasing the power to said blower drive motor in response to signals from said sensors corresponding to a predetermined degree of blockage of said one or more filters.
 13. The method according to claim 9 wherein said cyclonic separator comprises: a vertical cylindrical tube provided with an inlet and exit opening to allow air to be drawn therethrough in an up direction; connecting a set of stationary vanes in each of the upstream and downstream portions of the tube and sized and positioned to direct the air flowing therethrough in a cyclonic path through the tube such that mist in the air therein migrates outwardly to and in the downstream direction along the inside wall of the tube; positioning a drain hole near the downstream end of the collection chamber.
 14. The method according to claim 9 including sensing an increase in said air flow from said booth and transmitting a corresponding signal to a VFD controller connected to cause an increase in power to said blower drive motor.
 15. The method according to claim 9 including sensing the vacuum within said booth and generating a corresponding signal and transmitting the same to a VFD controller to increase or decrease the power to said blower drive motor so as to substantially maintain a predetermined vacuum level therein sufficient to substantially prevent the escape of air in said booth.
 16. The method according to claim 9 further including detecting opening movement of an access door panel and generating a corresponding output signal and transmitting the same to a VFD controller so as to cause an increase in blower drive motor power to increase the rate of air flow drawn from said booth upon opening of an access door panel.
 17. A demister apparatus for eliminating mist generated in a machine tool installation having a booth with one or more access door panels which are opened for loading and unloading parts therein but closed during a cycle of machining of said parts, comprising: a blower having a drive motor continuously drawing a flow of air out of said booth to maintain a partial vacuum in said booth sufficient to prevent the escape of air containing mist from said booth; an exhaust duct system connected to receive said air flow drawn out of said booth; a remote demister apparatus including one or more filters connected to said exhaust duct system and including said blower when operated drawing an air flow out of said booth, said drawn out air flow passing through said one or more filters in said remote demister apparatus and thereafter exhausted through an outlet; and an arrangement increasing the power to said drive blower motor when an increase in air pressure in said booth occurs or is imminent which would otherwise reduce the vacuum level therein to counteract the effects thereof, said arrangement including a VFD controller associated with said drive motor, said VFD controller increasing said drive motor power in order to increase the air flow drawn out of said booth.
 18. A method for eliminating mist generated in a machine tool installation having a booth with one or more access door panels which are opened for loading and unloading parts therein but closed during a cycle of machining of said parts comprising: a blower connected to said booth and operated with a drive motor so as to continuously draw a flow of air out of said booth to maintain a partial vacuum in said booth sufficient to prevent the escape of air containing mist from said booth; connecting an exhaust duct system to receive said air flow drawn out of said booth; providing a remote demister apparatus including one or more filters connected to said exhaust duct system receiving said air flow out of said booth and passing said air flow through said one or more filters in said remote demister apparatus and thereafter exhausting said air flow through an outlet; and increasing the power to said blower motor when an increase in air pressure in said booth occurs or is imminent which would otherwise reduce the vacuum level therein to counteract the effects thereof including installing a VFD controller associated with said drive motor so as to increase said drive motor power. 